1. Field of the Invention
The present invention relates to coating material used for antistatic high refractive index film formation, as well as to an antistatic/anti-reflection film covered transparent laminated body and an antistatic/anti-reflection film covered cathode ray tube using this coating material.
In particular, the present invention relates to coating material for antistatic/high refractive index film formation which is useful as coating material for transparent substrate surfaces requiring prevention of electrostatic charge and/or prevention of reflection, such as, for example, display screens of display apparatuses, covering materials for these surfaces, window glass, glass for show windows, display screens of TV Braun tubes, display screens of liquid crystal devices, covering glass for gauges, covering glass for watches, windshield and window glass for automobiles, and image display screens of cathode ray tubes, as well as to antistatic/anti-reflection film covered laminated bodies composed of antistatic/high refractive index films using this coating material and low refractive index films, and to cathode ray tubes, at least the image display of which comprises this transparent laminated body, and which are provided with various functions such as antistatic functions, electromagnetic wave shielding functions, anti-reflection functions, and image contrast improvement functions and the like.
2. Background Art
Electrostatic charge builds up easily in transparent substrates for image display, for example, in image display parts of TV Braun tubes, and as a result of this electrostatic charge, a problem is known wherein dust gathers on the display screen. Furthermore, problems are known wherein external light is reflected in the image display screen, or external images are reflected, and thus the images on the display screen become unclear.
In order to to solve the above-described problems, conventionally, a fluid in which finely powdered tin oxide doped with antimony (ATO) was dispersed in a nonaqueous solvent such as the hydrolyric product of silicon alkoxide (hereinbelow termed silica sol) was applied and desiccated to form an antistatic film on, for example, the surface of a transparent substrate, and a low refractive index film having a refractive index lower than that of the antistatic film was then formed on this antistatic film. That is to say, using a coating material comprising a non-aqueous dispersion fluid containing a mixture of the antimony doped tin oxide fine powder described above and silica sol, an antistatic film was formed, and on this, a coating material comprising a nonaqueous dispersion fluid of silica sol was applied and a low refractive index film was formed.
Furthermore the cathode ray tube which forms the TV Braun tube or the display of a computer or the like displays characters or images or the like by causing an electron beam from an electron gun to impact a fluorescent screen which emits red, green, and blue light. This cathode ray tube radiates an electromagnetic wave as a result of the emission of this high voltage electron beam, and there are cases in which undesirable effects are exerted on human beings or machines in the vicinity thereof. Furthermore, when the electron beam collides with the fluorescent body or bodies, a static charge is generated on the front surface of the faceplate.
Conventionally, in order to solve the above problems, a transparent and electrically conductive oxide film comprising, for example, indium oxide or the like, was formed by the sputtering method or the vapor deposition method on a faceplate, and this faceplate was applied to the front surface of the face panel and thus electromagnetic wave shielding was conducted; alternatively, a transparent and electrically conductive film was formed by coating the front surface of the face panel with a silica type binder dispersion fluid containing antimony doped tin oxide and silica sol or the like, and an antistatic effect was imparted to the front surface of the face panel. Furthermore, as shown in the following formula, in order to improve image contrast, cathode ray tubes were proposed in which colorants such as pigments or the like were included in the antistatic coating fluid, and thus antistatic effects and an increase in contrast were achieved.
C.sub.r =(.pi.B/RT.sub.g L)+1
C.sub.r : contrast PA2 B: fluorescent screen brightness PA2 T.sub.g : light transmittance of glass PA2 L: external light illumination PA2 R: fluorescent screen reflectivity
Furthermore, cathode ray tubes have also been proposed in which colored antistatic coating fluids are applied by being sprayed onto the display screen, and a film with surface irregularities is thereby formed, thus providing the cathode ray tube with an anti-reflection effect as a result of light scattering.
The refractive index of the conventional antistatic film described above is within a range of n=1.50 to 1.54, and the difference between this refractive index and the refractive index of the low refractive index film which is formed by means of the hydrolytic product of silicon alkoxide (silica sol) is small, so that accordingly, the anti-reflection effect created by means of the combining of such a conventional antistatic film and a low refractive index film is insufficient, and such a product was thus not suitable for practical application.
Furthermore, cathode ray tubes which were obtained by a method in which a faceplate having formed thereon a transparent and electrically conductive film such as, for example, indium oxide or the like, by means of the sputtering method or vapor deposition method, was applied to a display screen, are extremely expensive. Moreover, in cathode ray tubes having applied thereto an antistatic/optical filter, obtained by a method in which a colored antistatic fluid was coated thereon, possess insufficient electric conductivity, so that sufficient electromagnetic shielding effects could not obtained, and furthermore, in the case of cathode ray tubes having applied thereto antistatic/optical filter/anti-reflection functions formed by means of a method in which colored antistatic coating fluid was applied by spraying, as a result of these surface irregularities of the film which was thus formed, a problem existed in that as a result of the surface irregularities of the film which was thus formed, the degree of resolution of the images declined sharply.